Optical pumping velocity selective

The Stimulated Raman laser bears a superficial resemblance to an optically pumped gas phase molecular laser, but with one crucial difference. The Optically Pumped Laser (OPL) is a three level system (Koffend and Field, 1977). The PUMP transition is e v J <— e"v"J" and the lasing transition is e v J — evJ. If the pump laser is monochromatic, it selects a particular velocity in the e v J upper laser level. Thus there is a negligible Doppler width... 

Since the homogeneous width y of the Lamb-dip profile increases with pressure p, the maximum allowed deflection angle e in (8.1) also increases with p. A comparison of pressure-induced effects on the kernel and on the background profile of the Lamb dips and on the Doppler profile therefore yields more detailed information on the collision processes. Velocity-selective optical pumping allows the measurement of the shape of velocity-changing coUisional line kernels over the full thermal range of velocity changes [979]. 

Investigations are under way to combine a cesium beam atomic clock with laser optical pumping, replacing the A and B magnets of conventional clocks by two laser-beam-Cs-beam crossing regions. There would be no spatial selection of atoms with certain velocities as occurs with the A magnet. The preliminary results support the potential of this technique... 

To date, two specific phase-space optical-pumping schemes have been demonstrated. One uses a two-photon Raman transition and the other is based on the velocity-selective coherent population-trapping (VSCPT) effect. 

The following is an example of one of the many possible applications of optical pumping to a time-of-flight spectrometer with velocity selection for molecules in defined quantum states in supersonic beams [10.241. 

Saturation spectroscopy is based on the selective saturation of an inhomo-geneously broadened molecular transition by optical pumping with a monochromatic tunable laser. As has been outlined in Sect.3.6 the population density n. (v )dv of molecules in the absorbing state is selectively depleted of molecules with velocity components... 

In saturation spectroscopy, a monochromatic laser beam labels a group of atoms within a narrow range of axial velocities through excitation or optical pumping, and a Doppler-free spectrum of these selected atoms is observed with a second, counterpropagating beam. 

An alternative approach to forced flow is to seal the layer with a flexible membrane or an optically flat, rigid surface under hydraulic pressure, and to deliver the mobile phase to the layer by a pump [9,41,43-46]. Adjusting the solvent volume delivered to the layer optimizes the mobile phase velocity. In the linear development mode, the mobile phase velocity (uf) will be constant and the position of the solvent front (Zf) at any time (t) after the start of development is described by Zf = Uft. The mobile phase velocity no longer depends on the contact angle and solvent selection is unrestricted for reversed-phase layers in forced flow, unlike capillary flow systems. 

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